package niuke;

import java.util.Scanner;

public class 不要二 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int w = scanner.nextInt();
        int h = scanner.nextInt();
        int result = 0;

        int w_4 = w /4 ;
        int w_4_yu = w%4;

        int h_4 = h/4;
        int h_4_yu = h%4;

        //奇数行
        result = result + (w_4*2 + (w_4_yu>2?2:w_4_yu))*h_4*2;
        //偶数行
        result = result + (w_4*2 + (w_4_yu<=2?0:1))*h_4*2;

        if(h_4_yu != 0){
            if(h_4_yu<=2){
                result = result + (w_4*2 + (w_4_yu>2?2:w_4_yu))*h_4_yu;
            }
            else {
                result = result + (w_4*2 + (w_4_yu>2?2:w_4_yu))*2;
                result = result + w_4*2 + (w_4_yu<=2?0:1);
            }
        }

        System.out.println(result);
    }
}
